1 Geog 357: Data models and DBMS

Geographic Decision Making

Ways of storing digital data File structures –simple –ordered sequential –indexed Data models Databases –hierarchical –network –relational

File structures Basic terms –record data items related to a single logical entity (e.g. a student record) (row in a table) –field a place for a data item in a record (first name field in a student record) (column in a table) –file a sequence of records of the same type (the table)

File structures 3 Smith Jane A 1 Wood Bob C 2 Kent Chuck B 4 Boone Dan B ID Last First Grade record field A file: “STUDENT”

File structures Simple list –list of entries in which the order of entry into the list determines the order of the list 3 Smith Jane A 1 Wood Bob C 2 Kent Chuck B 4 Boone Dan B ID Last First Grade

File structures Search of a simple list entails going through each record until search is satisfied (linear search), which is inefficient 3 Smith Jane A 1 Wood Bob C 2 Kent Chuck B 4 Boone Dan B ID Last First Grade

File structures Ordered sequential files –list of entries ordered in some way (e.g. numerically or alphabetically) 1 Wood Bob C 2 Kent Chuck B 3 Smith Jane A 4 Boone Dan B ID Last First Grade

File structures Search of an ordered sequential list can use a binary search method - but only for the ordered field 1 Wood Bob C 2 Kent Chuck B 3 Smith Jane A 4 Boone Dan B ID Last First Grade

File structures Indexes provide a reference to records based on an index field, which is ordered Boone * Kent * Smith * Wood * 1 Wood Bob C 2 Kent Chuck B 3 Smith Jane A 4 Boone Dan B ID Last First GradeLast Pointer

Data models A data model is a particular way of conceptually organizing multiple data files in a database –hierarchical –network –relational

Hierarchical data model Class Student Grade Instructor ID Parent-child relationship (one-to-one or one-to-many) among data Department

Hierarchical data model Advantages easy to search can add new branches easily Disadvantages must establish the types of search prior to development of the hierarchical structure

Network data model Class Student Grade Instructor ID One-to-one, one-to-many, many-to-one, or many-to-many relationships possible Department

Network data model Advantages flexible, fast, efficient Disadvantages complex restructuring can be difficult because of changing all the pointers

Data models Hierarchical and network data models have generally been replaced by the relational data model Relational databases (and their derivatives) dominate the (non-GIS) database market: Oracle, Informix

Databases A database is a collection of data files that is structured (organized) to facilitate data storage, manipulation, and retrieval. A database management system (DBMS) is a software package that performs these database functions

Why Databases?? Shift from computation to information – Focus on the way to structure information Datasets increasing in diversity and volume. – Digital libraries, interactive video, e-commerce –... need for DBMS exploding DBMS encompasses most of the information technology – OS, languages, theory, multimedia, logic, web ?

Database - Definition A very large, integrated collection of data. A shared collection of logically related data designed to meet the information needs of an organization Models real-world enterprise – Entities (e.g., students, courses) – Relationships (e.g., Madonna is taking CS564)

Database - Definition Three key elements of database definition: –Shared –Interrelated –Predefined applications Side notes: –Database is NOT the real world Database is an abstraction –Database  Information Data becomes information only when they are used to provide answers to queries

Database Management System (DBMS) DBMS: A software system that enables users to define, create, and maintain the database and which provides controlled access to this database. Provide a layer between user application programs and the data –Data Definition Language (DDL) –Data Manipulation Language (DML)

File-based Processing

Problems with File-based Systems Inconsistencies!Same data is stored in multiple places. Inconsistencies! We need to write special programs for each user question Data can be corrupted due to system crash while change is made. User programs are not easy to share data or evolve.

Database Management System (DBMS)

Advantages of Database Approach Control of data redundancy –Have a central depository of all data and their descriptions –Same information stored only once Data Integrity Controlled access to database Data independence Concurrent Access Crash recovery

Disadvantages of DBMS Complexity Cost of DBMS software, hardware and data conversion Performance Higher impact of a failure When NOT to use DBMS? No data sharing Small scale Real-time constraints

Roles in the Database Environment Data Administrator (DA) Database Administrator (DBA) Database Designers (Logical and Physical) Application Programmers End Users (native and sophisticated)

Summary Databases are collections of inter-related data. DBMS used to maintain, query large datasets. Benefits include recovery from system crashes, concurrent access, quick application development, data integrity and security. The advantages and disadvantages of DBMSs. The personnel involved in the DBMS environment Database management is one of the broadest, most important areas in IST.